Pulse shape modifying circuit



PULSE SHAPEMODIFYING CIRCUIT Aug. 2, 1949.

S. H. M. DODINGTON PULSE SHAPE MODIFYING CIRCUIT 2 Sheets-Sheet 2 Filed Oct. l0, 1945 A TTOR/VE'Y Patented ug. 2, 1.949

PULSE SHAPE MoDiFYING CIRCUITY Sven H. M. Dodington, Nutley, N. J., assignor to Federal Telephone and Radio CorporatiomNew York, N. Y., a corporation of Delaware Y Application October 10, 1945, Serial No. 621,578 Claims. (Cl. Z50-27) This invention relates to circuits for modifying the shape of pulses and more particularly vto circuits to be used for modifying the shape of a series of significant pulse waves as for instance encountered in radio obstacledetection systems andthe like.

In my copending application, Ser. No. 551,470,

vfiled: August 28, 1944, I disclose a system for intercepting radio impulses transmitted by radio locating systems and for transmitting in response thereto simulated reflections as might bef obtained from obstacles such as aircraft and ships. The receiver of the system includes a pulse repeating system which upon the reception of a transmitted impulse produces a series of significant pulses which are sent out in sim` ulation of reflected pulses that mightV be expected from the normal reflection characteristics of an object or group of objects.

It is an object of the present invention to provide an improved means for producing the simulated reflection pulses to more closely resemble actual reflection pulses.

Y It is another object of the present invention to provide a circuit for modifying the shape'of a series of signicant pulses.

It is another object to provide a circuit for shaping a series of pulses which have been produced in response to a transmitted impulse so as to simulate the reflections that might be expected of a given number of ships or aircraft.

In accordance with my present invention, I

provide for a system which produces simulated reflection pulses as disclosed in the aforesaid application, a double stage intermediate frequency amplifier which is arranged to be keyed on by the application of a square wave to the screens of the amplifying tubes thereof. .The unblocking pulse is applied to the first stage of the amplifier simultaneously with the application of the Ywave of simulated reflection pulses. .The applied unblockng pulse is also subjected to the action of a differentiating circuit which is arranged to affect the bias of the second stage whereby the resultant output thereof is modified in amplitude in accordance with the differentiated value of the said unblocking pulse. As a consequence the normally strong reflections at vthe start of the pulse wave are reduced in amplitude to simulate the exact characteristics of actual reflection pulses. By the proper proportioning of various circuit parameters most any desired shape of the ultimate pulse waves may be obtained.

These and other features and objects of this invention will'become'more apparent upon consideration of the following detailed description ages and pulses at various points in thev amplifier of Fig'. 2. Y

ReferringA now to the drawings the repeater system of Fig.' 1 which has been fully described in my copending application, Ser. No. 551,470 referred to hereinabove, comprises a two-way antenna l which is connected to a transmitterreceiver comprised of a coupling unit 2 connected to an input converter 3 wherein the radio frequency or ultra-high frequency of the carrier of the incoming radio pulses is beat down to a supersonic frequency by heterodyning against the output of a local oscillator 4 for application to a wide band intermediate frequency amplifier stage 5. Connected to an output connection 6 of the intermediate frequency stage 5 is an output intermediate frequency amplifier 1 which feeds into an output converter B. Here, the intermediate frequency carrier energy-to which has been added simulated repeat pulse energy from a supersonic repeat pulse generating device or cell 9, in accordance with the showing in the aforesaid application Serial No. 551,470, and coupled to the output connection 6, is recon- Verted to the original incoming impulse carrier frequency by heterodyning against the output of the oscillator 4. Thek output converter 8 is connected to supply the coupling unit 2 feeding into the antenna l now functioning in its transmission capacity. A keying circuit |0 receiving a'controlled impulse vvfrom a demodulator Il of the output of the amplifier 5 supplies Va suitable keying potential both to the output amplifier 1 and to the input amplifier 5 for the unblocking and blocking of the operation of the two ampliers respectively. This has the purpose of providing the proper sequence of reception and transmission for the system as a Whole. It is to be understood, of course, Vthat the demodulator Il may be of any suitable form capable of performing the keying function as outlined. VThe keying pulses themselves may be obtained from circuits such asa multivibrator circuit which is triggered by the incoming impulse as disclosed in my copending application, Ser. No. 480,603, filed: March 26, 1943. Y

Referring now to Fig. 2 the intermediate fre-V being obtained over doubly couplingcoils or transformers I5 and I6 respectively. The tun-r ing of the single interstage coil I4 may be acscomplished by known arrangementsfof any suitable type such as a variometer 'or' known plungertuned coil, as disclosed in the said Patent No.

. '4 blocking tube I3 with the unblocking pulses from line 2|, the output from transformer I6 associated with tube I3 is produced only during the unblocking intervals, regardless of what transient or noise effects may be present in the previous stage between the Vblocking intervals.

It is thus vseen that the gain in the tube I3 is modid so that the strong reflections at the start of transmission are reduced rin amplitude. By suitably proportioning the resistances II and I9 and the condenser I8 almost any desired resultant shape of the pulse Vseries may be ob-V tainedas Yfor instance suggested in graph c 2,357,442. The double' coils YI5 and I6 may be of. a conventional predetermined xed design Vtuned to operate withinA a speciiied .frequency band, distributed vcapacities being sufficient to tune the coils without the use of bridgig'trim- Y mer condensers., Other c ircuitelements are 'of Y suchrating as toproduce in cooperation with the coils a frequency responsejcurve in accordance Vwith the respective requirements. The circuit incorporates certain gain modifying elements which includes a decoupling resistance I 'I Y in the plate circuit of the pentodeJZ; ai con- 'denser .I8 between the coupling coil I4 andthe pentode I3, and a resistance I9 in the circuit from the condenser VI8 to ,ground at 20. An

unblocking pulse is applied from .circuit I0 over4 a connection 2l to screengrids 22 and 23 of the pentodes I2 and I3, respectively. The plates Yof the pentodes I 2y and I3 areenergizedfrom a source of B+ at 24, the formen over the resist- Vance Il and the latter over aresistance 25. The input 'to thetube I2, as available in vthe Yprimary ofthe transformer I5, is. shown in graph a and includes an incoming .pulse. 26 and pulse reflections 21. as obtained from the repeatercell which shows ai series of pulses as they are normally desired .in order to suitably simulate Vreflections from agroup of obstacles. These latt'er are, of course, obtained vafter subjecting the pulses in the secondary of the transformer I6 to operations which willVA eliminate their effective negative portions. Y Although I have .described'iny inventil il? connectionl with simulated radio obstacle detection systems, lit will, of course, be apparent that the pulse shape modifying system here 4difsc'zlos'ed'is equally usable in connection with any other applicationwhich calls vfor the reshaping of 'one `or more pulses in accordance with the method disclosed.

While I have `described above the principles of my invention in Vconri'ection with specic apparatushit is to be clearly'iinder'stood that this desc'riptionis made only by way 'of example 'and 'not 9. As the tube I2 isv unblockedby the square.

wave of graphcwhichis timed sofas to eliminate the incoming pulsejz, the vsimulated reection pulses 21 are amplified to appear in the plate circuit of the tube I2 as shown at 28 in graphy b. the pulses of graph b so as to attenuate the leading pulses as indicated in 'graph c whichillustrates closely Vthe true reflections vof a groupof obstacles such as a squadronof aircraft or ships.

It is desirable however, to reshape This reshapingV will now be described, e J

The resulting intermediate frequency voltage across the tuning coil yI II will appear as shown in graph d. The application of the positiveV square wave (graph e)- to the screen 2 2 apart from making'the tube I2 operative causes a-Y Vnegative square wave to be established across thev resistance I1 inaccordane with the form shown in graph f. This negative square wavev undergoes a differentiation in the circuit formed by thecapacity I8 and the resistance I9 to as- Y sume a. form 4in accordance withrgraphiy. `Accordinglythe tube I3 `becomes biased somewhat negatively at the start ofthe transmission cycle .whereby its gainis reduced. AThe resulting voltage on the grid of tube I3 combining the applied series of reilection 'pulses as at Yd and the differ-j entiated unblocking pulse in accordance with 'graph'g will take the form shown in vgraph .Theji-lnal form of the 'pulse series as it `iivillap- 'pear' in lthe secondary o'fxtlieY transformerv I6 asa limitation of4 th scope of myi'nv'entionfas defined in the objects and the .accompanying claims. Y

lclalmr. f..

l. A circuit for modifying tli'e shape oi pulse waves appliedthereto, comprising ni'ea'nsfor amplifying pulse waves yon a carrier of a'certainrquency, means for rendering operative "said amplifying means by the application'thereto o`f ya lperiodic unblockin'g wave, and 'means inclfi'd'ed rin said amplifying rnearis'to change 'the shape of saidunblocking wave and t'co'mbine the changed Munblockin'g Vwave with the amplified pulsewav'es.

2. A circuit according vto claim 1 wlei'nsaid arnpnfying means' comprises 'a r'standascond amplifying stage, 'and said .means 'f or remercie operative said amplifying means yis lconnected to said rst and said second stage.

f 3. A Circuit according to. jciaim 1 @grassen amplifying means comprise'sua first and lsecond .amplifying Stege', and mamans. fr. .Changing vthe shape Aof the unblocking lwavevisincludedA in J.pling inductance across Vwhich is derived a voltage wave which is substantially the inverse of thesa'id unblockingwave. 5V-v` A circuit according to claim'l wherein said Vamplifying means comprisesafirst and arsecond amplifying stage, said rst. stageV including acouv'phng inductance across which is derivedayoltage wave'which is'substantially the inverse vofthe's'aid unblocking wave, and'saidmeansto change shape ofthe unblocking wave includes aidifferentiating circuit includedin the couplingbet'ween said two stages, whereby .the inverse Avoltage wave Spro- Vduced by differentiationis 'applied'to said second stage together with theampiined puisewaves.

6. A circuit for modifying the'sha'pe of Axpulse [waves applied thereto comprising input coupling will takethe form indicated in graph i. By une means, a first amplifying stage, a second amplifying stage, output coupling means for said second stage, interstage coupling means intermediate said two stages, a diiferentiating circuit between said interstage coupling means and said second stage, and means for applying an unblocking voltage wave to said rst and second stages.

7. A circuit according to claim 6 wherein said input and said output means comprise double coil means and said interstage coupling means comprises single coil means.

8. A circuit according to claim 6 wherein said rst and said second stages each comprise a pentode, the plate circuit of said rst stage including a coupling inductance across which a voltage from said unblocking wave is derived.

9. A circuit according to claim 6 wherein said iirst and second stages each comprise a pentode, said means for applying an unblocking wave being connected to certain grids of said two pentodes.

10. A circuit for modifying the shape of pulse waves applied thereto on a certain carrier frequency, comprising a tuned frequency input transformer, a first pentode amplifying stage, a second pentode amplifying stage, an interstage single coupling coil intermediate said pentodes, a decoupling resistance in the plate circuit of said first pentode, a voltage differentiating circuit intermediate said single coupling coil and said second pentode a tuned frequency output transformer for said second pentode, and circuit means for applying an unblocking voltage wave to certain grids of said pentodes,

SVEN H. M. DODINGTON.

REFERENCES CITED The following referenlces are of record in the le of this patent:

UNITED STATES PATENTS OTHER REFERENCES Ultra High Frequency Techniques, by Brainerd et al., July 1942, chapter 3. (Copy in Division 51.) 

